Method for increasing the yield of recoverable monocyclic aromatic hydrocarbons in thermal hydrodealkylation processes



United States Patent C) 3,160,671 METHOD FOR mCREASlNG 'IHE YELD FRECOVERABLE MONOCYCLEC ARGMATIC HYDRQiIARBGNS 1N THERMAL HYDRODE-ALKYLATION PROQESSES Stanford I. Feigelman, Haddonfield, N..l., andEugene Aristotl, Newtown Square, Pa, assignors to The Atlam tic RefiningCompany, Philadelphia, Pa, a corporation of Pennsylvania No Drawing.Filed Mar. 16, 1961, Ser. No. 94,675 1 Claim. (Cl. 260-672) Thisinvention relates to a method for hydrodealkylating alkylated monocyclicaromatic hydrocarbons. More particularly, this invention isconcerned'with increasing the yield of recoverable monocyclic aromatichydrocarhens in the thermal hydrodealkylation processes.

The process of subjecting hydrocarbon fractions containing alkylatedmonocyclic aromatic hydrocarbons to high temperatures and pressures inthe presence of hydrogen in a reaction zone devoid of catalyticallyactive material in order to hydrodealkylate the alkylated monocyclicaromatics to benzene has long been known.

The instant invention is concerned with an improvement to theaforementioned process whereby the yield of recoverable monocyclicaromatic hydrocarbons from the hydrodealkylation process is increased.

It is an object of this invention to increase the yield of recoverablemonocyclic aromatic hydrocarbons in a process of thermalhydrodealkylation of an alkylated monocyclic aromatic-containinghydrocarbon fraction.

It is a further object of this invention to increase the yield ofrecoverable monocyclic aromatic hydrocarbons in a process of thermalhydrodealkylation of a toluenecontaining hydrocarbon fraction.

It is a further object of this invention to increase the yield ofrecoverable monocyclic aromatic hydrocarbons in a process of thermalhydrodealkylation of toluene.

Additional objects of this invention will be apparent from thedescription and claim that follow.

The present invention may be described briefly as a method forincreasing the yield of recoverable monocyclic aromatic hydrocarbons,particularly benzene and toluene, from a normally liquid hydrocarboncharge fraction containing alkylatecl monocyclic aromatics in a thermalhydrodealkylation process. This is accomplished by subjecting analkylated monocyclic aromatic hydrocarboncontaining fraction, togetherwith diphenyl hydrocarbons, to temperatures ranging from 950 F. to l450F. in a reaction zone devoid of catalytically active material, i.e.thermal conversion. In addition to the elevated temperatures, the feedhydrocarbons together with the added dipehnyl hydrocarbons are subjectedto pressures ranging from 400 pounds per square inch to 10,000 poundsper square inch for times ranging from 1 second to 600 seconds in thepresence of hydrogen in amounts ranging from 1.0 to 20.0 moles ofhydrogen per mole of the normally liquid hydrocarbon charge to thereactor, i.e. both feed and diphenyl hydrocarbons, based on the averagemolecular Weight of these hydrocarbons charged. The unconsumed hydrogenis separated from the reactor efiluent and recycled to the reaction zonetogether with makeup hydrogen.

It will be noted that the recycle hydrogen may contain small amounts ofnormally gaseous hydrocarbons such as methane, but these hydrocarbonsare not included in the calculation of the amount of normally liquidhydrocarbon charge to the reactor. The amount of hydrogen consumed bythe reaction depends to a considerable degree upon the particular chargehydrocarbons employed. In general, however, this amount will be at least1 mole of hydrogen per mole of monocyclic aromatic hydrocarbonconverted. A portion or all of the diphenyl hydrocarbons contained icein the etliuent from the reactor likewise may be recycled to thereaction zone together with any makeup diphenyl hydrocarbons that may berequired for the purpose of this invention.

The diphenyl hydrocarbons suitable for use in this invention includediphenyl, methyl diphenyl, diphenyl methane, diphenylenemethane(fiuorene), dimethyl diphenyl, methyl diphenyl methane, diphenyl ethane,diphenyl benzene and similar hydrocarbons, and including mixtures of twoor more of these hydrocarbons. The amount of diphenyl hydrocarbonsintroduced into the reaction zone along with the alkylated monocyclicaromatic hydrocarbon-containing charge may vary between 1 mole percentand 15 mole percent based on the total moles of normally liquidhydrocarbon charge to the reactor.

The liquid product of the reaction after the removal of hydrogen isfurther fractionated to obtain the desired benzene product andseparately recover the alkylated monocyclics which can be recycled forfurther conversion to benzene. Thus, by recoverable monocyclic aromatichydrocarbons is meant benzene and alkylated monocyclic aromatichydrocarbons which can be recycled for ultimate conversion to benzene.

Although the hydrodealkylation process may be carried out within theprocess limits set forth above, some what narrower ranges of processconditions are preferred for optimum conversion with specific chargestocks. For example, in a preferred embodiment of this invention tolueneis hydrodealkylated to benzene at temperatures ranging between 1200 F.and 1400 F. at pressures ranging between 400 p.s.i. and 800 p.s.i., inparticular about 600 p.s.i., with reaction times of from 20 to 30seconds and particularly about 25 seconds utilizing hydrogen in anamount ranging from 2.5 moles of hydrogen per mole of normally liquidhydrocarbon charge to the reactor to 6 moles of hydrogen per mole ofhydrocarbon and, in particular, 4 moles of hydrogen per mole ofthe'normally liquid hydrocarbon charge. Under these conditions, it ispreferred to employ from 2 mole percent to 7 mole percent of diphenylhydrocarbons based on the total moles of normally liquid hydrocarboncharge to the reactor.

A variety of charge stocks may be employed for conversion by thermalhydrodealkylation in accordance with the instant invention. It isnecessary, however, that such charge stocks contain alkylated monocyclicaromatic hydrocarbons in order that the purposes of the invention may berealized, namely, increasing the yield of recoverable monocyclicaromatic hydrocarbons in a thermal hydrodealkylation process.

Charge stocks which contain these compounds and which may be utilized inthe process of this invention include virgin or straight-run hydrocarbondistillate fractions, furnace oil fractions boiling between about 300 F.and 650 F. resulting from the catalytic cracking or" a petroleum gas oilfraction, fractions obtained by the catalytic reforming of hydrocarbons,coal tar aromatic fractions and alkylated benzene hydrocarbons obtainedas a result of the alkylation of benzene to produce a starting materialfor alkyl aryl sulfonate production. The alkylated monocyclic aromatichydrocarbons include toluene, the Xylenes, ethyl benzene, trimethylbenzene such as mesitylene, higher alkylated benzenes wherein the alkylgroup may contain from 6 to 12 carbon atoms or more and wherein thebenzene ring may have additional alkyl side chains. It will beunderstood, of course, that with certain types of higher alkylatedmonocyclic aromatics wherein there are several side chains on the ringor where the side chain may be long it may not be possible to convertthe alkylated monocyclic into benzene in a single pass. In accordancewith this invention, however, the yield of recoverable monocyclicaromatics is increased with the result that the ultimate conversion tobenzene is increased, since the alkylated product from any single passmay be recycled.

The following example is provided to illustrate a specific embodiment ofthe invention.

EXAMPLE Two continuous alkylation runs were carried out in a tubularreactor which was devoid of catalytically active material. The chargecomposition, reaction conditions, and products obtained are set forth inthe table.

Table Run 1st 2d Charge Toluene-100 Toluene-96.9

mole percent mole percent;

Diphenyl- 3.1 mole percent Reaction conditions:

Temperature, F 1, 296 1, 290 Pressure, p.s.i 600 000 Reaction time, seen21. 2 21. 2 Mole ratio, H22 Hydrocarbon.. 4. 0 4.1 Monocyclic aromaticsrecovered in the product, mole percent:

Benzene 73. 3 37. 1 Toluene 22. 2 28. 9

It will be seen that in the run where no diphenyl was employed 95.5 molepercent recovery of benzene and toluene was obtained, showing that 4.5mole percent monocyclic ring compounds were lost. In the second runwherein diphenyl was used the charge contained 96.9 percent toluene anda recovery of benzene and toluene of 96.0 mole percent was obtainedshowing that apparently only 0.9 mole percent of monocyclic ringcompounds were lost. However, it was found by analysis that 0.45 molepercent of the diphenyl was lost which would correspond to a productionof 0.9 mole percent benzene so that the corrected value of monocyclicaromatics lost amounted to 1.8 percent. Thus, by comparing the runs itis apparent that by introducing diphenyl into the reaction zone anincrease of 2.7 mole percent of recoverable monocyclic aromaticcompounds was obtained. Since toluene is recycled to extinction in acommercial process it will be seen quite readily that in a recycleoperation if an increase of 2. percent of recoverable aromatics isobtained per pass, the instant invention provides a method of markedlyincreasing the total recovery of benzene in a hydrodealkylation process.

We claim:

In a process for hydrodealkylating alkylated monocyclic aromatichydrocarbons in an alkylated monocyclic aromatic-containing hydrocarbonfraction wherein such fraction is subjected to thermal conversion in areaction zone devoid of catalytically active material in the presence ofhydrogen at a temperature ranging from 950 F. to 1450 F. at a pressureranging from 400 pounds per square inch to 10,000 pounds per square inchfor a time ranging from 1 second to 600 seconds with the amount ofhydrogen ranging from 1.0 to 20.0 moles of hydrogen per mole of thenormally liquid hydrocarbon charge, the improvement which comprisesincreasing the yield of recoverable monocyclic aromatic hydrocarbons byintroducing diphenyl into the reaction zone together with the alkylatedmonocyclic aromatic-containing hydrocarbon fraction, said diphenyl beingin an amount ranging from 1 mole percent to 15 mole percent based on thetotal moles of normally liquid hydrocarbon charge to the reaction zone,and recovering the monocyclic aromatic hydrocarbons.

References Cited in the file of this patent UNITED STATES PATENTS1,230,975 Alexander June 26, 1917 2,335,596 Marschner Nov. 30, 19432,739,991 Hervert Mar. 27, 1956 2,929,775 Aristofi et al. Mar. 22, 1960UNITED STATES- PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,160,671 December 8, 1964 Sta'nf ordfL, Eeigelm'an er; 'al. It ishereby certified. that err or appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column 4, line 8 for- R2," ead 2.7

Signed and sealed this 20th day of'April 1965.

(SEAL) Attest:

ERNEST W. SWIDER- I EDWARD J BRENNER Attesting Officer Commissioner ofPatents Notice of Adverse Decision in Interference In Interference No.95,417 involving Patent No. 3,160,671, S. I. Feigelman and E. Aristofi,METHOD FOR INCREASING THE YIELD OF RECOV- ERABLE MONOCYCLIC AROMATICHYDROCARBONS IN THER- MAL HYDRODEALKYLATION PROCESSES, final judgmentadverse to the patentees was rendered June 14, 1973, as to claim 1.

[Ofiicz'al Gazette July 2, 1,974.]

